The present invention relates to an optical object identification apparatus for detecting the type of objects without contact, and also relates to a printing apparatus and an object classification apparatus using the same.
Copying apparatuses and printing apparatuses that conduct recording processing while conveying recording media are being developed to achieve high function, high-speed processing and high resolution, and the recording media used thereby are of varied types including plain paper, glossy paper and OHP (Overhead Projector) sheets. When images are printed on such widely varying recording media by means of a printer (especially an ink jet printer) that is an image recording apparatus, it is necessary, for forming high-quality images, to execute recording control corresponding to the respective recording media because the infiltration rate and the dry time of an ink are different depending on the type of the recording media.
Conventionally, as methods for detecting the type of recording media including paper media such as printer paper, as well as resin films and sheets, there have been a mechanical detection method, a thermal detection method and an optical detection method. The mechanical detection method is for detecting the type of a recording medium by the displacement amount of a contact and the like when the recording medium is inserted into a conveyor portion. The thermal detection method is for detecting the type of a recording medium by placing a thermal element on the recording medium and detecting the thermal change of the recording medium or of the heating element itself.
In the optical detection method, a light emitting device and a light receiving device are provided, and a recording medium is irradiated with light from the light emitting device so that the type of the recording medium is detected by the amount of reflected light from the recording medium. For example, in “Paper Kind Detector and Image Forming Device Provided with the Same” disclosed in Japanese Patent Laid-Open Publication HEI No. 10-198174, as shown in FIG. 15, the type of a paper sheet 3 is detected by the change of an output from a light receiving device 2 based on the placement angles of two light emitting devices 1a, 1b and the light receiving device 2 with respect to the paper sheet 3. Further, in “Identification of Recording Medium in a Printer” disclosed in Japanese Patent Laid-Open Publication No. 2000-301805, and in its equivalent U.S. Pat. No. 6,291,829 B1, as shown in FIG. 16, light from a transmission illuminator 11 passes a recording medium 12, light with a grazing incidence from a grazing illuminator 13 irradiates the recording medium 12, and light from a vertical illuminator 14 vertically irradiates the recording medium 12 via an amplitude beam splitter 15. Then, a surface image of the recording medium 12 is obtained by a photodetector array 16 such as CCD (Charge Coupled Device) and C-MOS (Complementary Metal Oxide Semiconductor) devices, and the obtained image is subject to two-dimensional image processing to identify the type of the recording medium 12.
Further, there is a method for detecting the type of recording media, in which a detection liquid containing a specified pigment or a fluorescent material is infiltrated into a recording medium, and light in the wavelength range absorbed by the pigment or the fluorescent material is irradiated to a portion of the recording medium infiltrated with the detection liquid to determine the intensity of reflected light, or infrared radiation is irradiated to measure the infrared absorption spectrum of reflected light (see Japanese Patent Laid-Open Publication No. 2001-88275 for example).
However, the above-mentioned conventional methods for detecting the type of recording media suffer a following problem.
That is, in the case of the mechanical detection method and the thermal detection method, a contact and a heating element should be brought into contact with a recording medium, which may disturb the movement of the recording medium during conveyance, and may also cause the deformation of the recording medium. Moreover, detection failure due to the deterioration of a contact section caused by wear may occur.
Further, in the case of the aforementioned optical detection methods, the type of a recording medium is detected by the difference in the amount of reflected light from the recording medium, and therefore detection may not be possible if the difference in the amount of reflected light is small, causing considerable restraint of detectable types of recording media. Furthermore, attention needs to be paid to the adjustment of placement angles of the light emitting device and the light receiving device, which makes assemblage of the apparatus complicated.
Furthermore, in the case of the method in which an image sensor such as CCD and C-MOS devices is used in a light receiving section, image processing becomes complicated, and pursuing higher identification accuracy increases the number of elements to be identified, thereby making the processing more complicated as well as making the light receiving device expensive. In the case of the method in which a detection liquid is infiltrated into the recording medium at a portion to measure reflected light from that portion of the infiltrated medium, the recording medium is possibly given pigmentary change and fouling. In addition, this method requires a means for infiltrating the detection liquid, which causes growing in size of the apparatus, and measuring of the infrared absorption spectrum complicates the configuration and signal processing of the light receiving portion.